Magnetorheological fluids (MRF) fall within a category of smart materials being developed. Under an applied magnetic field, solid magnetizable particles in a magneto-rheological fluid are in chainlike alignment with magnetic lines connected between the north pole and the south pole and thus produce resistance to a shear stress.
Conventional magneto-rheological fluid brakes are, basically, cylindrical in shape, and each essentially comprise a housing and a disc body. The disc body is surrounded by magnetically permeable blocks (or silicon steel plates) of a symmetric C-shaped cross-section. Coils are wound around the magnetically permeable blocks (or silicon steel plates) to generate an applied magnetic field. A magneto-rheological fluid is evenly distributed in the space between the disc body and the magnetically permeable blocks.
Referring to FIG. 1, there is shown a cross-sectional view of a conventional magneto-rheological fluid brake 9. As shown in the drawing, the conventional magneto-rheological fluid brake 9 is characterized in that: an axle 92 and a disc body 93 which are connected to each other are axially disposed in a housing 91; the disc body 93 is surrounded by magnetically permeable blocks 94 (or silicon steel plates) of a symmetric C-shaped cross-section; a coil 95 is wound around the magnetically permeable blocks 94 (or silicon steel plates) to generate an applied magnetic field; and a magneto-rheological fluid 96 is evenly distributed in the space between the disc body 93 and the magnetically permeable blocks 94.
The magnetically permeable blocks 94 of a symmetric C-shaped cross-section is a limiting factor in the area of magnetic permeability of the magneto-rheological fluid 96 under an applied magnetic field, and in consequence a braking force exerted in the direction of magnetic lines indicated by the arrows shown in FIG. 1 is relatively weak.
In addition, the conventional magneto-rheological fluid brake 9 comprises one and only one said 95; hence, when the coil 95 is damaged or severed, the brake 9 undergoes a loss of the applied magnetic force and thereby causes a complete failure of the braking force, which poses a serious threat to vehicle safety.
Accordingly, it is imperative to invent a magneto-rheological fluid brake effective in enlarging the area of magnetic permeability of a magneto-rheological fluid under an applied magnetic field to increase a braking force and preventing a complete failure of the braking force.